From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF97FC43382 for ; Thu, 27 Sep 2018 16:06:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D07A216FE for ; Thu, 27 Sep 2018 16:06:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8D07A216FE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728485AbeI0WY6 (ORCPT ); Thu, 27 Sep 2018 18:24:58 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:45181 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727212AbeI0WY6 (ORCPT ); Thu, 27 Sep 2018 18:24:58 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0T9a0AL0_1538064340; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T9a0AL0_1538064340) by smtp.aliyun-inc.com(127.0.0.1); Fri, 28 Sep 2018 00:05:43 +0800 Subject: Re: [v2 PATCH 2/2 -mm] mm: brk: dwongrade mmap_sem to read when shrinking To: Vlastimil Babka , mhocko@kernel.org, kirill@shutemov.name, willy@infradead.org, ldufour@linux.vnet.ibm.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1537985434-22655-1-git-send-email-yang.shi@linux.alibaba.com> <1537985434-22655-2-git-send-email-yang.shi@linux.alibaba.com> <33d52132-546f-3c8a-3445-cdbc9068589a@suse.cz> From: Yang Shi Message-ID: <4bcdb16d-902e-55ed-5f5d-12c5ba7cbdfd@linux.alibaba.com> Date: Thu, 27 Sep 2018 09:05:37 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <33d52132-546f-3c8a-3445-cdbc9068589a@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/27/18 5:14 AM, Vlastimil Babka wrote: > On 9/26/18 8:10 PM, Yang Shi wrote: > > Again, "downgrade" in the subject > >> brk might be used to shinrk memory mapping too other than munmap(). > ^ shrink > >> So, it may hold write mmap_sem for long time when shrinking large >> mapping, as what commit ("mm: mmap: zap pages with read mmap_sem in >> munmap") described. >> >> The brk() will not manipulate vmas anymore after __do_munmap() call for >> the mapping shrink use case. But, it may set mm->brk after >> __do_munmap(), which needs hold write mmap_sem. >> >> However, a simple trick can workaround this by setting mm->brk before >> __do_munmap(). Then restore the original value if __do_munmap() fails. >> With this trick, it is safe to downgrade to read mmap_sem. >> >> So, the same optimization, which downgrades mmap_sem to read for >> zapping pages, is also feasible and reasonable to this case. >> >> The period of holding exclusive mmap_sem for shrinking large mapping >> would be reduced significantly with this optimization. >> >> Cc: Michal Hocko >> Cc: Kirill A. Shutemov >> Cc: Matthew Wilcox >> Cc: Laurent Dufour >> Cc: Vlastimil Babka >> Cc: Andrew Morton >> Signed-off-by: Yang Shi > Acked-by: Vlastimil Babka > > Same nit for the "bool downgrade" name as for patch 1/2. Will solve in next version. Thanks, Yang > > Thanks, > Vlastimil